Epsilometer Test-Based Determination of Susceptibility of Clinically Important Candida Isolates to Conventional Antifungal Agents

One hundred thirty yeast clinical isolates comprised of 81 C. albicans, 22 C. tropicalis, 11 C. parapsilosis, 9 C. glabrata and 7 C. krusei were evaluated for antifungal susceptibility using the E-test. MIC, MIC50 and MIC90 of amphotericin B (AMB), flucytosine (FC), fluconazole (FL), itraconazole (IT) and voriconazole (VOR) were determined at 24 and 48 h of incubation and compared with data obtained by the broth microdilution method. MIC and MIC90 determined at 24 h for C. albicans were: AMB<=0.002-0.064, 0.032, FC 0.023-2.0, 0.75, FL 0.064->256, 64, IT 0.012-2.0, 0.19 and VOR 0.008-0.750, 0.047. Those for C. glabrata were: AMB 0.016-4.0, 1.25, FC<=0.06-4.0, <=0.06, FL 1.0->256.0, 64.0, IT 0.003-4.0, 1.0 and VOR 0.047-2, 0.38. Overall, Candida species remain uniformly susceptible to AMB and FL; this not withstanding the finding that C. glabrata and C. krusei showed significant resistance to FL. MICs after 48 h of incubation were higher than those determined at 24 h of incubation; increased resistance rates and enhanced endpoint trailing particularly with FL and IT were also evident. Overall agreement between the MICs obtained by the E-test and broth microdilution methods was >=86% within ±2 dilution for AMB, FL and VOR for C. albicans, C. tropicalis and C. parapsilosis and 67% for C. glabrata and 52% for C. krusei for FL. Based on the 24 h MICs determinations, resistant strains in Candida species from Jordan were encountered at a range of 8-22% against azole antifungals tested. These results suggest that the E-test is simple, inexpensive, easy both to read and interpret and has a good correlation to the CLSI microdilution test and can be conveniently incorporated and performed in a hospital-based clinical laboratory.